A biological clock is housed within the brain of the fruit fly. In insects, reptiles and mammals these brain-based clocks govern temporal organization at many levels ranging from the regulation of gene activity in highly specialized tissues to overt periodic behaviors such as 24-hour cycles of activity and rest. Few clues exist with regard to the biochemical composition of such biological pacemakers, but clock mutants are available in Drosophila melanogaster, and these offer a means of probing the mechanism in great detail. We will be analyzing the molecular composition and function of the per locus. This gene appears to be expressed in the brain and establishes temporal organization within the fly through the action of a diffusible substance. Our approach will be as follows. 1) DNA corresponding to the per locus will be isolated and mutations defining the gene will be placed on the physical map. 2) Transcribed sequences at the per locus will be identified and related to the genetic and physical maps. 3) Protein coding sequences will be identified at the per locus and will be used to generate per-peptides in Escherichia coli. These peptides will be used to generate antibody which will in turn facilitate the characterization per protein with respect to size and distribution. 4) The possibility that the per locus encodes the humoral factor coupling the pacemaker to the rest of the organism will be tested. 5) An attempt to identify the biochemical form of the pacemaker will start with a search for temporal regulation in the synthesis of per RNA and protein.